Update CHANGES.md

Author: mosuka

CHANGES.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
-## [Unreleased]
+## [v0.2.0] 2020-03-19
 
 - Add join endpoint #19 @mosuka
 - Add leave endpoint #18 @mosuka